Parasite humour

Parasite of the month

Lepeophtheirus salmonis

Salmon lice are parasitic copepods that feed on the skin and blood of salmonids. Over their life-cycle, they alternate between free-swimming, stationary and mobile life-styles. They attach to salmonids during the thrids life stage and grow up to 12mm for adults females (30mm with egg strings) and 6mm for adult males. Mean generation time is about 6 weeks at 12°C.


In small amounts, lice cause little damage to the fish but high intensities of infection can reduce growth and even lead to death of the host. Symptoms include skin erosion, constant bleeding and open wounds, which can facilitate infections by pathogens. Moreover, salmon lice are also vectors of a few pathogens, such as infectious salmon anemia.


In the recent years, their numbers have been increasing due to the growth of the aquaculture industry. High densities of hosts at fish farms was shown to increase transmission and to trigger the evolution of higher virulence of L. salmonis, as discussed in Mennerat et al. (2012 J. Evol. Biol.). This can have dramatic consequences for wildlife as (1) infestations of sea lice in salmon farms increases the number of lice in the rest of the surrounding water and because (2) lice act as a vector for diseases between wild and farmed salmon, affecting the evolution of virulence of parasites of wild fish.


Recently, a study by Losos et al. (2010 Behaviour) found stickleback to feed on female salmon lice - towards new management practices at fish farms?


(source for picture: http://www.bears-and-more.de/grafiken/2010-12-03_1.jpg)

Parasite of the month

Cystidicola spp.

Cystidicola are parasitic nematodes infecting many fish species throughout the northern hemisphere. Their life-cycle  involves two hosts: an amphipod as first intermediate host and a fish as definitive host. Amphipods become infected by accidentally feeding on the eggs of the parasite. The eggs hatch inside the host and undergoes two molts in the hemocoele before becoming infective to fish. When a fish feeds on an infected amphipod, the parasite migrates from the gut to the swim-bladder where sexual reproduction will take place. The eggs are then produced, enter the gut via the pneumatic duct and ultimately released into the water with the faeces of the host.

Black (1983 Can J Fish Aquat Sci 40: 643-647) discussed the possibility that intensive fishing of the lake trout Salvelinus namaycush in the Great Lakes of North America may have caused a decline in Cystidicola stigmatura infections over the 20th century. In particular, inspection of museum specimens revealed that trouts caught before 1925 were more often infected with the nematode than trouts caught after 1925. This is particularly interesting for stock management as maintaining fish populations below a threshold could limit transmission for some parasite species and improve filet quality. More about this here.

(source for picture: http://img-fotki.yandex.ru/get/9810/133242081.6a/0_ed45e_dbb3331_XL.jpg)

Parasite of the month

Pelseneeria spp.

Pelseneeria are small parasitic snails belonging to the Eulimidae family. They feed on sea urchins by the use of a proboscis which extends into the body cavity of their host.

In their study, Sonnenholzner et al. (2011 Ecology 92: 2276-2284) highlight how over-fishing can deeply affect food webs and thereby parasites.

Pelseneeria snails are preys of the crab Mithrax nodosus in the Galapagos. Increased fishing pressure on the predators of the crab has thus benefited the crab populations, leading to a decrease in the prevalence of the parasitic snail. Under these circumstances, sea urchins are benefiting from over-fishing.

Accordingly, the authors reveal in another study (Sonnenholzner et al. 2009 Mar. Ecol. Prog. Ser.) the impact of sea urchins on algae and anemones. Hence, environmental disturbances can have drastic cascading effects on the whole ecosystems in which parasite can play a crucial role.


(source for picture: http://www.conchology.be)

Current ideas in marine parasitology

7 challenges & 5 solutions

The International Symposium on the Ecology and Evolution of Marine Parasites and Diseases organized by David Thieltges and Matthias Wegner has been held at NIOZ in Texel - NL on 10-14 March 2014. Among the various topics discussed during the symposium, Robert Poulin initiated the discussion on the integration of parasitology into marine ecology.

Robert Poulin identified 7 potential challenges to come over in order to reach this goal:

1-More parasites in marine ecology

Parasites are still largely ignored in ecology despite their importance as regulators of populations (Anderson & May 1981 PhilTransSocLB), as preys (Johnson et al. 2010 TREE, Goedknegt et al. 2012 eLS) and in terms of biomass (Dobson et al. 2008 PNAS, Kuris et al. 2008 Nature). Taking this part of biodiversity in marine biology would benefit theory.

2-More marine ecology in parasitology

Parasitologists have also typically ignored important discoveries in marine ecology that could help understanding host-parasite interactions in marine systems. Robert Poulin gave the example of ocean acidification that was emphasized in marine ecology but remained largely ignored by parasitologists in their research (MacLeod & Poulin 2012 Trends Parasitol.).

3-Maintain parasite discovery rate

 Even if many parasites are known, most of parasitic diversity remains to be discovered (the rate of discovery is still very high). This is currently accentuated with recent findings of cryptic species of parasites (e.g. Miura et al. 2006 PNAS, Rellstab et al. 2011 MEEGID). Discovering new species of parasites could help us estimating the importance of parasites in ecosystems and the structuring of parasite communities.

4-Elucidate parasite life-cycles

As pointed in section -3, the life-cycles of many parasites remain to be discovered: elucidating the transmission routes used by pathogens to spread within host populations is challenging and remains a central aim of epidemiology. Elucidating the life-cycles of parasites could improve the theory and help managing diseases (e.g. Dash & Vasemägi 2014 DAO).

5-More model parasite systems

Only a few parasite species are model systems (e.g. daphnia their microsporidia parasite Pasteuria ramosa, threespine stickleback and the tapeworm Schistocephalus solidus, salmonids and their lices). This is very contrasting with the diversity of parasites (and of their life-cycles) and questions about the relevancy of these models to represent most parasitic organisms.

6-Go offshore and go deep

We don't know much about the diversity of parasites offshore and in the deep sea nor their role in these ecosystems and much of the research has focused so far on parasites in coastal ecosystems. Going offshore and deep would help in getting a wider view of the importance of parasite in marine systems.

7-Tweak epidemiology for the sea

The epidemiological framework has been developed for terrestrial organisms. Hence it is possible that adapting epidemiological models to marine systems (e.g. by including water thickness in dispersion parameters) could lead to different predictions than in the terrestrial environment.

Robert Poulin ended up his presentation with 5 simple solutions to these challenges:

1. -More parasites in marine journals

2. -Keep up with the key ideas of other fields

3. -Support taxonomy and basic life cycle research

4. -Study new model parasite systems

5. -Tweak epidemiology for the sea

How to improve rearing conditions of salmon to re-stock natural populations

Petra Rodewald is currently defending her PhD thesis at the University of Helsinki. The thesis aims at improving rearing and release methods of salmons to improve the success of introduction of farmed salmon to re-stock natural stocks.

Link for the thesis: https://helda.helsinki.fi/bitstream/handle/10138/40333/rodewald_dissertation.pdf?sequence=1

 

Bye-bye lab fish!

Re-post 10.2012

I just completed my experiment with Diplostomum sp. parasites and lab-reared sticklebacks. I took care of the fish during the last two years. A bit sad this period of my life ended but released it is over :)

Some nice pics of these spiny stuffs: